The invention relates to the field of transmission of digital data. More specifically, the invention relates to the encoding of attribute data into the parity or error check symbols for main data, i.e., the addition of additional data symbols to the data symbols of the digital data being transmitted which are the error check symbols encoded with the information of the attribute data to be conveyed, and later recovery of said attribute data from the transmitted main data combined with its attribute encoded error check symbols.
In the field of transmission (this includes video tape recording which in the video arts is considered equivalent to transmission) of digital data, it is common to use error check symbols or parity symbols which are generated from the data being transmitted and which are used on the receiver side of the link to improve the reliability of the transmission process. These error check or parity symbols are usually digital bits when binary code is used, but may also be symbols having more than two values for codes other than binary. The error check or parity symbols will hereafter be referred to as error check symbols. They are generated in many different known ways. Generally, the generation of error check symbols involves the use of error correcting codes which translate the main data to be transmitted or recorded into one or more error check symbols. In linear error correcting codes, this is done by dividing the polynomial represented by the main data by an error check polynomial and using the remainder as the error check symbols. Many different error correction codes are known to do this translation process some of which are linear and some of which are not linear. Those skilled in the art appreciate the difference between linear and nonlinear codes.
After the error check symbols are generated, the main data and the error check symbols are combined and transmitted to the receiver. Hereafter, the main data to be transmitted without any error check symbols appended thereto will be referred to as the main data while the main data with the error check symbols appended thereto will be referred to as the transmitted data. The main data with the error check symbols appended thereto and encoded with the attribute data will be referred to hereafter as the attribute encoded transmitted data and the main data error check symbols encoded with the attribute data will be hereafter referred to as the modified error check symbols.
In the prior art at the receiver, the transmitted data is decoded to generate what is called a syndrome. If there were no errors in the transmission process, the syndrome will indicate this condition, usually by being all zeros in the binary code case. If there were errors, the syndrome will so indicate. Furthermore, if the error was within the range of error correction of the error check symbols, the location of the error will be indicated by the syndrome. The range of error correction is controlled by the number of error check symbols that are appended to the main data and is the number of errors which can occur and be corrected by use of the error check symbols although any number of errors can be detected but may not be correctable because they exceed the error correction range. Depending upon the number of symbols in error and the number of check symbols generated, the error check symbols may be decoded with the main data to allow correction of errors of less than a certain number of symbols and detection of some errors having a greater number of symbols in error. Generally, the use of a higher number of check symbols for a given number of main data symbols will increase the reliability of the error detection and error correction process.
In certain digital systems, a set of separate and dedicated data symbols are commonly used to identify certain attributes of the main data that is to be transmitted. Hereafter, this separate and dedicated data will be called "attribute data". As an example of what attribute data typically is, in color television signal transmission and processing systems of a digital nature, the attribute data can be the horizontal sync-to-color subcarrier burst phase for every TV scanning line. This phase relationship is not specified in the color television signal. It is a value that must be calculated based upon the detected relative times of occurrence of a certain time in the horizontal synchronization pulse and the beginning of the color subcarrier burst. In digital video applications, this phase relationship may be calculated on the transmitter side.
In the prior art, it has been common to separately encode such sync-to-color subcarrier burst phase for every TV scanning line into a few symbols of data. These attribute symbols are then added to the group of video sample data words that belong to this same horizontal scanning line. The data words defining the video (and usually the synchronization signals) for each horizontal scanning line plus its associated attribute data are then transmitted. Upon reception of the transmitted data, the sync-to-color subcarrier burst phase information identified by the attribute symbols is used to facilitate the processing of the accompanying video data.
The difficulty with this approach is that in transmitting the attribute data in addition to the main data, a certain portion of the bandwidth of the transmission channel must be devoted to the transmission of the attribute data, and, in the case of storage, certain physical space on magnetic media or like memory is required for the attribute data. Bandwidth in transmission channels and space in storage memories is usually at a premium, and it is advantageous to save bandwidth in transmission channels and space in storage memories in any possible manner.
Accordingly, a need has arisen for a technique of encoding attribute data in digital data which enables transmission and recovery of the attribute data without the addition of attribute data symbols to the transmitted data, i.e., without transmitting attribute data symbols in addition to the main data and the error check symbols.